1. Field of the Invention
The present invention relates in general to a marine engine, and more particularly to an anode system for a marine engine.
2. Description of Related Art
Outboard motors often power sea-faring boats. Large internal combustion engines of these motors drive propellers to propel the boat. Such engines produce a lot of heat and are housed within a poorly ventilated cowlings that protect the engines from the corrosive effects of salt water.
Outboard motors usually employ an open-loop cooling system to maintain the engine temperature below a particular degree. Such cooling systems commonly draw water into the outboard motor through a water inlet on a submerged lower unit, and circulate the water through the engine block, cylinder head, exhaust manifold and exhaust guide. Saline water, however, can cause the engine components to corrode, especially due to the dissimilarities of metals in the engine and the exhaust system, and the electrically conductive nature of salt water.
One means for reducing the corrosive effects associated with using salt water as a coolant is to provide a sacrificial anode within one or more of the cooling passages of the engine. Sacrificial anodes are typically employed to retard the corrosive effects of salt water on an engine block. The anti-corrosion effect is also useful in preventing galvanic corrosion resulting from differences in the materials (e.g., iron and aluminum) comprising the engine and the exhaust system.
Salt water within an anode-protected cooling system tends to corrode and dissolve the anode to the exclusion of the metal block and cylinder head. To facilitate this effect, the anode is typically formed from a material which more readily releases electrons than the metal forming the cylinder block and cylinder head (i.e., it has a lower oxidation potential). The anode, comprised of a "sacrificial metal," thus corrodes rather than the metal forming the engine. An outboard motor engine thus often includes several sacrificial anodes that are provided within the coolant passages in the cylinder block, adjacent to the engine cylinders.